The present invention relates to a patterned substrate and a liquid crystal display provided therewith. The patterned substrate referred to herein means an electrically conductive material patterned substrate.
As office automation equipment such as a personal computer and the like has been made portable in recent years, it has become important to manufacture a display device in use for such office automation equipment at a low cost. This display device is formed by interposing a display medium having an electrooptic property between a pair of substrates having electrodes formed thereon. Display is performed by applying a voltage between these electrodes to change the electrooptic property of the display medium.
An active matrix type display device is becoming mainstream because of its display performance. In the active matrix type display device, each pixel is provided with a switching element capable of increasing the number of scanning lines. With techniques that enable the number of the aforementioned scanning lines and the like to increase, higher resolution, higher optical contrast, more gradations and wider visibility angle are being achieved.
In the active matrix type liquid crystal display, pixel electrodes are electrically connected via active elements (the aforementioned switching elements). The active elements include a two-terminal nonlinear element (MIM) and three-terminal nonlinear element. The active element typically used now is a thin film transistor (TFT), which is a three-terminal nonlinear element.
With increase in demand for electrodes with low power consumption in recent years, a reflective liquid crystal display and a reflective/transmissive liquid crystal display are increasingly developed instead of a transmissive liquid crystal display, which usually requires a backlight.
In order to obtain a bright display in the reflective liquid crystal display, the reflective electrode area is enlarged. Further, as a reflective electrode, an Al film is formed on a resin film having a plurality of concave and convex portions formed thereon to scatter an incident light. Also, wiring for transmitting picture signals and a driver for driving a liquid crystal display are connected by using ITO (indium-tin oxide) used for transparent electrode portions or the like for the purpose of preventing higher resistance due to oxidation during post-processing.
The above-described conventional liquid crystal display, however, has problems as described below. That is, when a reflective electrode is formed by forming an Al metal film on a resin film having a plurality of concave and convex portions formed thereon as described above, it is impossible to partially form an Al metal film, particularly in a mass production process, unless a special film forming method such as mask-deposition or the like is used. Therefore, the Al metal film is formed over the entire surface of a liquid crystal display panel including ITO portions such as terminal portions for connecting the wiring and the driver, transparent electrodes and the like. However, the following problem is caused when this reflective electrode film (Al metal film) is patterned.
When the Al film is etched into a prescribed shape in a state that the ITO film and the Al film are laminated, a photolithography process is performed. In this case, when an exposure and a development are performed to form a resist film, an battery is constituted between the ITO film and the Al film since an alkaline developer is used. As a result, the Al film and the ITO film are corroded and melted and thereby the yield decreases. This phenomenon, which is called electrolytic corrosion, occurs not only in the case of combination of an ITO film and an Al film, but occurs in any combination that causes a battery reaction by using an alkaline developer.
In order to solve this problem of electrolytic corrosion, there is a proposal that an Mo (molybdenum) film is formed before a metal film such as Al or the like is formed to make a two-layer structure. According to this technique, an Al layer and an Mo layer can be successively formed. Also, since the two layers can be etched simultaneously by using a liquid mixture composed of phosphoric acid, nitric acid, acetic acid and water, a reflective electrode film (Al film) can be patterned without increasing the number of processes or causing electrolytic corrosion.
By the way, in the case of patterning a metal film such as Al or the like formed on the resin film as a reflective electrode or a transparent conductive film, the metal film often peels because the adhesion between the resin film and the metal film is weakened due to the swelling of the resin film by a resist remover. The aforementioned Mo layer also peels from the resin film when a peel test is performed after the Mo film is formed on an acrylic resin and patterned. As a result, the yield decreases.
In general, in the case where metal wiring is provided on an insulator such as a polymeric film or the like, the problem is that the adhesion between the polymeric film and the metal film is weak. Thus, various attempts have been conventionally made. For example, it is revealed that sputtering is more effective than vapor deposition to obtain strong adhesion when the metal film is formed. However, there is a problem that sufficient adhesion cannot be obtained even by sputtering when the aforementioned Mo film is formed.